ARS | Publication request: SUSTAINABILITY OF NATURAL RUBBER-PRODUCING CROPS IN THE UNITED STATES: APPLIED BIOTECHNOLOGY LESSONS 2000-2010

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 31, 2010
Publication Date: September 18, 2010
Citation: Mcmahan, C.M., Shintani, D.K., Cornish, K., Coffelt, T.A., Ray, D.T., Whalen, M.C. 2010. Sustainability of Natural Rubber-Producing Crops in the United States: Applied Biotechnology Lessons 2000-2010. Association of the Advancement of Industrial Crops (AAIC) 22nd Annual Meeting, 2010 New Crops: Exploring Diversity, Preserving our Future, Fort Collins, CO, September 18-22, 2010.

Technical Abstract: Natural rubber (NR) is a critical and strategic raw material for industrial manufacturing and national defense. Development of a US-based supply of NR is recognized in the Critical Agricultural Materials Act, Public Law 95–592. Domestic rubber-producing crops have been introduced in the US during times of short supply and high prices; however, development was discontinued once prices of imported NR fell. During the past ten years guayule has been re-introduced as a new crop in the southwestern US; Russian dandelion is under research and development as a rubber-producing crop for the northern US. However, commercial sustainability of domestic natural rubber is limited by yields of NR from existing germplasm. During the past ten years the tools of biotechnology have been applied to address this issue. Rubber biosynthesis takes place via the isoprenoid pathway to a metabolic endpoint, i.e., rubber is stored, not metabolized, by plants. The polymerization reaction proceeds by successive condensations of the monomer isopentenyl pyrophosphate (IPP) following initiation by an allylic pyrophosphate (APP). A lipid monolayer membrane stabilizes the insoluble, high molecular weight (>106 g/mole) rubber. Most of the rubber biosynthesis pathway enzymes are well established, with the exception of the rubber transferase (RuT). Assumed to be a cis-prenyl transferase, it may actually be an enzyme complex, evidence of which has emerged through systematic biochemical and molecular studies. Many proteins associated with rubber particles yet not directly involved in the rubber biosynthesis pathway have now been identified. The role of these proteins may be in the structure of the rubber particle membrane. Genomic information has been developed and disseminated to benefit researchers worldwide. Transformation systems have been developed for guayule and Russian dandelion, and manipulations of known pathway genes successfully completed. Laboratory results are not always predictive of field evaluations in guayule, supporting the strong influence of environment on rubber production. Strategies to improve the efficacy of metabolic engineering have evolved with that of the biotechnology toolbox including more effective promoters, multiple gene constructs, and chloroplast transformation.